Image forming apparatus and control method thereof

ABSTRACT

An image forming apparatus includes a transport part which includes a transport belt to transport a printing medium, an image forming part which transfers a toner to form a color image, and a controller which controls the image forming part to form a test image for color registration of the image forming part on the transport belt while an image is formed for a plurality of printing media. Thus, both a test image and a plurality of printed media are formed during a single printing process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Korean Patent Application No.10-2006-0130916, filed on Dec. 20, 2006 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Apparatuses and methods consistent with the present general inventiveconcept relate to an image forming apparatus and a control methodthereof, and more particularly, to an image forming apparatus whichperforms an improved color registration process using a test image and acontrol method thereof.

2. Description of the Related Art

An image forming apparatus such as a laser printer exposes aphotosensitive member, develops a toner, and transfers and fuses thetoner to a printing medium such as a paper, thereby forming an image.

Generally, an image forming apparatus to form a color image includes animage forming part which has a laser scanning unit (LSU) providedcorresponding to a plurality of colors, and a plurality ofphotosensitive members and transfer rollers, etc. The plurality ofphotosensitive members are arranged along a transport path of a printingmedium transported by a transporting means such as a transporting belt.

The image forming apparatus forms an image for color registration(hereinafter, referred to as a test image) other than an actual image inorder to adjust an image forming characteristic (hereinafter, referredto as color registration) of the image forming part, e.g., determinationof a developing condition, color registration, etc.

Conventionally, the color registration is performed in an initializingprocess when the image forming apparatus is provided with power or afterthe predetermined number of papers is printed.

In the color registration, an image of data is not printed (hereinafter,referred to as printing data). Rather, a test image is formed. The testimage is not formed during a printing process for the printing data, butis formed during the aforementioned initializing process before start ofthe printing process or after completion of a predetermined number ofthe printing process.

Thus, a lengthy period of time transpires from when the image formingapparatus is supplied with power until a first printing output isobtained (hereinafter, referred to as a first page output time). Inother words, the time to obtain a printing output is delayed.

Further, if the color registration is performed separately from theprinting process, a color discordance occurring in the actual printingprocess may not be properly reflected on the color registration.

SUMMARY OF THE INVENTION

The present general inventive concept provides an image formingapparatus which has an improved printing speed by minimizing delay dueto color registration and a control method thereof.

The present general inventive concept also provides an image formingapparatus which improves accuracy and reliability of color registrationby reflecting a color discordance which may be generated in a printingprocess and a control method thereof.

Additional aspects and utilities of the present general inventiveconcept will be set forth in part in the description which follows and,in part, will be obvious from the description, or may be learned bypractice of the present general inventive concept.

The foregoing and/or other aspects and utilities of the present generalinventive concept can be achieved by providing an image formingapparatus comprising: a transport part which comprises a transport beltto transport a printing medium; an image forming part which transfers atoner to form a color image; and a controller which controls the imageforming part to form a test image for color registration of the imageforming part on the transport belt while an image is formed for aplurality of printing media corresponding to a single printing process.

The image forming part may comprise: an engine which performs anexposure process for the toner to be developed and transferred; a videocontroller which generates video data based on printing datacorresponding to the image being formed on the printing medium or testdata corresponding to the test image; and an engine controller whichoperates the engine on the basis of the video data generated by thevideo controller.

The engine controller may comprise: an auto color registration (ACR)controller which performs the color registration of the image formingpart according to a result of sensing the test image.

The image forming apparatus may further comprise a data storage partwhich stores the test data, wherein the video controller reads out thetest data stored in the data storage part through direct memory access(DMA).

The data storage part may further store the printing data.

The foregoing and/or other aspects and utilities of the present generalinventive concept can also be achieved by providing an image formingapparatus comprising: an engine which transfers a toner to form a colorimage; a video controller which generates video data; an enginecontroller which operates the engine according to the video datagenerated by the video controller; and a controller which controls thevideo controller to generate video data based on printing data or testdata by determining whether to perform a printing process to form animage on a printing medium or to perform color registration of theengine.

The engine controller may comprise an auto color registration (ACR)controller which performs the color registration of the engine accordingto a result of sensing the test image formed corresponding to the testdata.

The image forming apparatus may further comprise a data storage partwhich stores the test data, wherein the video controller reads out thetest data stored in the data storage part through direct memory access(DMA).

The data storage part may further store the printing data.

The foregoing and/or other aspects and utilities of the present generalinventive concept can also be achieved by providing a control method ofan image forming apparatus which comprises a transport part having atransport belt to transport a printing medium and an image forming partto transfer a toner to form a color image, the control methodcomprising: controlling the image forming part to form an image on afirst printing medium among the plurality of printing mediacorresponding to a single printing process; controlling the imageforming part to form a test image for color registration of the imageforming part on the transport belt after forming the image for the firstprinting medium; and controlling the image forming part to form an imageon a second printing medium among the plurality of the printing mediaafter forming the test image.

The image forming part may comprise an engine which performs an exposureprocess for a toner to be developed and transferred; a video controllerwhich generates video data; and an engine controller which operates theengine according to the video data generated by the video controller,the controlling the image forming part to form the image on the firstprinting medium, the transport belt and the second printing mediumcomprising controlling the video controller to generate video data basedon printing data or test data for color registration by determiningwhether the image forming part performs the printing process to form theimage on the printing medium or the color registration.

The engine controller may comprise an auto color registration (ACR)controller which performs the color registration of the image formingpart, the control method may further comprise controlling the ACRcontroller to perform the color registration of the image forming partaccording to a result of sensing the test image.

The image forming apparatus may further comprise a data storage partwhich stores the test data, the controlling the image forming part toform the test image comprising controlling the video controller to readout the test data stored in the data storage part through direct memoryaccess (DMA).

The data storage part may further store the printing data, thecontrolling the image forming part to form the image on the firstprinting medium and the second printing medium comprising controllingthe video controller to read out the printing data stored in the datastorage part through direct memory access (DMA).

The foregoing and/or other aspects and utilities of the present generalinventive concept can also be achieved by providing a control method ofan image forming apparatus which comprises an engine to transfer a tonerto form a color image, a video controller to generate video data and anengine controller to operate the engine according to the video datagenerated by the video controller, the control method comprising:determining whether to perform a printing process to form an image on aprinting medium or to perform color registration of the engine; andcontrolling the video controller to generate video data based onprinting data or test data respectively corresponding to the determinedprinting process or color registration.

The engine controller may comprise an auto color registration (ACR)controller which performs the color registration of the engine, thecontrol method may further comprise controlling the auto colorregistration controller to perform the color registration of the engineaccording to a result of sensing the test image formed corresponding tothe test data.

The image forming apparatus may further comprise a data storage partwhich stores the test data, the controlling the video controller togenerate the video data may comprise controlling the video controller toread out the test data stored in the data storage part through directmemory access (DMA).

The data storage part may further store the printing data, thecontrolling the video controller to generate the video data comprisingcontrolling the video controller to read out the printing data stored inthe data storage part through direct memory access (DMA).

The foregoing and/or other aspects and utilities of the present generalinventive concept can also be achieved by providing an image formingapparatus comprising an image forming part which forms a color image fora plurality of printing media, and a controller which controls the imageforming part during a printing process to form a test image for colorregistration after forming an image on a first printing medium andbefore forming another image on a second printing medium.

The image forming apparatus may further comprise a controller whichoutputs a control signal to form the test image within an idle timeduring the printing process.

The image forming apparatus may further comprise an engine whichperforms an exposure process for a toner to be developed andtransferred; a video controller which generates video data based onprinting data corresponding to the image being formed on one of theplurality of printing media or test data corresponding to the testimage; and an engine controller which operates the engine based on videodata generated by the video controller.

The image forming apparatus may further comprise the video controller,wherein the video controller reads out the test data stored in a datastorage part during the printing process.

The image forming apparatus may further comprise the video controller,wherein the image forming part forms the test image for colorregistration during the first printing medium output time during theprinting process.

The engine controller may further perform the color registration duringthe printing process.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and utilities of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of the exemplary embodiments, taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram to illustrate a configuration of an imageforming apparatus according to an exemplary embodiment of the presentgeneral inventive concept;

FIG. 2 is a cross-sectional view of a transport part according to anexemplary embodiment of the present general inventive concept;

FIG. 3 is a block diagram illustrating a configuration of an imageforming part according to an exemplary embodiment of the present generalinventive concept;

FIG. 4 illustrates a margin between two consecutive printing mediums ina printing process;

FIG. 5 is a timing diagram illustrating a control sequence of acontroller according to an exemplary embodiment of the present generalinventive concept;

FIG. 6 illustrates a memory map of printing data and test data stored ina data storage part according to an exemplary embodiment of the presentgeneral inventive concept; and

FIG. 7 is a flowchart illustrating an operation of the image formingapparatus according to an exemplary embodiment of the present generalinventive concept.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentgeneral inventive concept, examples of which are illustrated in theaccompanying drawings, wherein reference numerals refer to theirassociated respective elements throughout. The exemplary embodiments aredescribed below in order to explain the present general inventiveconcept by referring to the figures.

FIG. 1 is a block diagram illustrating a configuration of an imageforming apparatus 100 according to an exemplary embodiment of thepresent general inventive concept. The image forming apparatus 100 maybe provided as a laser printer.

Referring to FIG. 1, the image forming apparatus 100 may include atransport part 110, an image forming part 120, a data storage part 130,and a controller 140.

The transport part 110 transports a printing medium, e.g., a paper, inaccordance with control signals from the controller 140. FIG. 2 is across-sectional view of the transport part 110 according to theexemplary embodiment of FIG. 1. The transport part 110 may include atransport belt 110 a, and transports a printing medium (not illustrated)by moving the transport belt 110 a. Referring to FIG. 2, the transportbelt 110 a transports the printing medium in a direction from A to A′,which is referred to as a printing medium transport path. Thus, thetransport belt 110 a movement corresponds to the printing mediumtransport path.

The image forming part 120 can form an image by transferring a toner tothe printing medium according to printing data. Referring to FIG. 2, theimage forming part 120 may include four sub-image forming parts 120 a,120 b, 120 c, and 120 d to correspond to respective colors such as cyan,magenta, yellow and black, respectively. The sub-image forming parts 120a, 120 b, 120 c and 120 d each can perform exposure, development andtransfer according to the printing data.

The image forming part 120 can form a test image for a colorregistration in accordance with control signals from the controller 140.The test image is formed on a surface portion (not illustrated) of thetransport belt 110 a based on test data. The test image may be formed tocorrespond to each of the sub-image forming parts 120 a, 120 b, 120 cand 120 d. For example, the test image may be formed as a sign or aletter.

Referring to FIG. 2, the image forming apparatus 100 may further includea sensor 150 which is provided on a path where the transport belt 110 amoves and senses light reflected to the test image. A result sensed bythe sensor 150 is delivered to the controller 140, and can be used forthe color registration.

The image forming apparatus 100 may further include a data storage part130 which stores printing data to be printed and test data to correspondto a test image. The image forming part 120 reads the printing data andthe test data in the data storage part 130 and performs a printingprocess and a color registration based on the printing data and the testdata.

The controller 140 controls the overall image forming apparatus 100. Thecontroller 140 controls the image forming part 120 to form an image on aprinting medium on the basis of the printing data. In addition, thecontroller 140 controls the image forming part 120 to form a test imageon the transport belt 110 a on the basis of the test data. In detail,the controller 140 controls the image forming part 120 to form the testimage while forming the image on a plurality of printing media in oneprinting process.

FIG. 3 is a block diagram illustrating a configuration of the imageforming part 120 according to the present exemplary embodiment. Theimage forming part 120 may further include a video controller 121, anengine controller 122 and a laser scanning unit (LSU) 123. The videocontroller 121 and the engine controller 122 may be provided as a chipon a printed circuit board (PCB) (not illustrated).

The data storage part 130 stores printing data 131 to be printed andtest data 132 corresponding to a test image for a color registration.The data storage part 130 may be provided as a synchronous dynamicrandom access memory (SDRAM), a read only memory (ROM), and other wellknown memory devices.

The video controller 121 receives the printing data 131 or the test data132 through direct memory access (DMA) to generate video data (VDO).

The engine controller 122 may include an auto color registration (ACR)controller 122 a and an LSU controller 122 b. The test image obtained bythe sensor 150 from the controller 140 is transmitted to the ACRcontroller 122 a, whereby it performs the color registration. The colorregistration is applied to a printing process immediately following thesensing of the test image.

The LSU controller 122 b converts video data (VDO) generated by thevideo controller 121 into output video data (VDO′) to the LSU 123 inorder to drive the LSU 123.

The Laser Scanning Unit (LSU) 123 scans the laser at a plurality ofphotosensitive members (not illustrated) provided in the sub-imageforming parts 120 a, 120 b, 120 c and 120 d according to the outputvideo data (VDO′) to form a latent image, thereby performing anexposure. A combination of the sub-image forming parts 120 a, 120 b, 120c and 120 d and the LSU 123 is provided as an example of an engine inthe present exemplary embodiment.

FIG. 4 illustrates a margin between two consecutive printing media(hereinafter, referred to as a paper) in one printing process. Thetransport belt 110 a transports a paper A and a paper B in a directionof B in the printing process. If a printing speed is 60 pages per minute(ppm), a margin between the papers A and B may be set at about 30% ofthe height H of the paper. For example, the height H of the papers A andB is about 270 mm (A4), and the margin M between the papers is about 80mm.

FIG. 5 is a timing diagram illustrating a control sequence of thecontroller 140 according to an exemplary embodiment of the presentgeneral inventive concept. The controller 140 can generate a controlsignal which is output to the image forming part 120 so that the imageforming part 120 can perform a printing process or form a test image.

Referring to FIG. 5, a control signal may include an FSYNC signal, anHSYNC signal, an SOD (Start Of Direct (Memory Access)) signal, an EOP(End Of Page) signal, an FSYNC (ACR) signal, an HSYNC (ACR) signal, anSOD (ACR) signal and an EOP (ACR) signal. In this case, the FSYNCsignal, HSYNC signal, SOD signal, and EOP signal correspond to aprinting process. Referring to FIG. 3, the control signal can be inputto the video controller 121 via the engine controller 122.

The FSYNC signal indicates a start of a printing process, and the HSYNCindicates a horizontal synchronous signal. For example, if a printingspeed is 60 ppm and A4 paper is provided, an interval between FSYNCsignals is 1 second. After the FSYNC, printing is performed in a unit ofthe line according to the HSYNC.

The SOD signal indicates a start of direct memory access (DMA) toprinting data. The video controller 121 starts DMA to the data storagepart 130 by an SOD after the FSYNC and reads out printing data 131stored in the data storage part 130.

FIG. 6 illustrates a memory map 130 a of printing data and test datastored in a data storage part 130 according to an exemplary embodimentof the present general inventive concept. If an SOD d₁ which indicates astart of DMA to printing data corresponding to the paper A is presentafter the FSYNC, the video controller 121 reads out printing data A 131a stored in the data storage part 130. Likewise, an SOD d₂ indicatesstart of DMA to printing data B 131 b corresponding to the paper B.

After 0.7 seconds from the FSYNC, the printing on the paper A iscompleted by the EOP to indicate completion of printing. There is aninterval of about 0.3 seconds from the EOP for the paper A to the FSYNCfor the paper B, which is referred to as an idle time when printing isnot practically performed.

In the present exemplary embodiment, the controller 140 outputs acontrol signal to the image forming part 120 to form a test image forcolor registration on the transport belt 110 a within the idle time.Regarding the control signal, the FSYNC (ACR), HSYNC (ACR), SOD (ACR)and EOP (ACR) correspond to forming the test image.

The FSYNC (ACR) indicates the start of forming a test image and isgenerated right after the EOP for the paper A. During the idle time, apolygon mirror (illustrated) provided in the LSU 123 keeps its rotationstate, and the HSYNC (ACR) is continually sensed. Thus, the videocontroller 121 reads out test data stored in the data storage part 130through DMA in the idle time as well as during the printing process.

In detail, after the FSYNC, if an SOD d_(a) which indicates start of DMAto test data is present, the video controller 121 reads out the testdata 132 a stored in the data storage part 130.

Then, the image forming part 120 completes forming a test image by anEOP (ACR) and starts printing paper B by a new FSYNC.

Provided that a period of an HSYNC is 450 μsec, a test image with 600 ormore lines may be formed in the idle time of 0.3 seconds.

As described above, since the color registration is performed during theprinting process, a first page output time (FPOT) is minimized, therebyimproving printing speed. Also, as compared with the color registrationwhich is performed periodically according to the accumulated number ofprinting papers, a delay time between processes is minimized.

Further, since the color registration can be performed under the sameconditions as the printing process, a discordance which may be generatedin the printing process is maximally reflected upon the colorregistration, thereby improving accuracy and reliability of the colorregistration.

Referring to FIG. 3, as the HSYNC is transmitted to the video controller121 via the engine controller 122, timing delays may arise (refer toHSYNC′ in FIG. 3), e.g., a gate delay in the engine controller 122 or awire delay in the printed circuit board (PCB).

In a present exemplary embodiment, a timing delay element which isgenerated in video data VDO and VDO′ is reflected on the colorregistration under the same conditions as the printing process. Thus, acomparatively accurate color registration as compared with the colorregistration can be performed independently from the printing process bythe engine controller 122.

Also, since the video controller processes the test data to form thetest image as well as the printing data, the ACR controller has a simpleconfiguration and a reduced cost in comparison to an ACR controllerhaving a separate configuration for processing test data.

Meanwhile, the test data, e.g., synchronous dynamic random access memory(SDRAM), can be stored in the data storage part and may be direct-memoryaccessed (DMA) by the video controller. Thus, various types of testimages may be formed as compared with test data residing in the enginecontroller 122.

FIG. 7 is a flowchart illustrating an operation of the image formingapparatus 100 according to an exemplary embodiment of the presentgeneral inventive concept. First, the controller 140 controls imageforming part 120 to form an image on a first printing medium in aprinting process which involves a plurality of printing media (operationS101). At operation S101, the controller 140 controls the videocontroller 121 to generate video data on the basis of printing datacorresponding to the first printing medium.

The controller 140 determines whether to perform color registration ofthe image forming part 120 (operation S102). If it performs the colorregistration at operation S102, the controller 140 controls the imageforming part 120 to form a test image on the transport belt 110 a(operation S103).

In FIG. 7, at operation S103, the controller 140 may output a controlsignal to the image forming part 120 to form the test image within theidle time of the printing process. Further, the controller 140 maycontrol the video controller 121 to generate video data on the basis oftest data for the color registration.

The controller 140 controls the ACR controller 122 a so that the imageforming part 120 can perform the color registration according to a testimage (operation S104) sensing result.

If operation S104 is performed or it is determined to not perform thecolor registration at operation S102, the controller 140 checks if theprinting process for all printing media is completed (operation S105).

If the printing process for all the printing media is not completed, thecontroller 140 controls the image forming part 120 to form an image on asubsequent printing medium among the plurality of printing media(operation S106). Then, operations S102 through S106 are repeated.

According to the present general inventive concept, since the colorregistration is performed during the printing process, a first pageoutput time (FPOT) is minimized to thereby improve a printing speed.Also, as compared with the color registration which is performedperiodically according to the accumulation number of printing papers,delay time between processes is minimized.

Further, since the color registration is performed under the samecondition as the printing process, a discordance which may be generatedin the printing process is maximally reflected on the colorregistration, thereby improving accuracy and reliability of the colorregistration. A timing delay element which is generated in a video datais reflected upon the color registration under the same condition as theprinting process, thereby performing comparatively accurate colorregistration.

Also, since the video controller processes the test data to form thetest image as well as the printing data, the ACR controller has a simpleconfiguration and reduced configuration costs.

Meanwhile, the test data can be stored in the data storage part, e.g.,synchronous dynamic random access memory (SDRAM), and may bedirect-memory accessed (DMA) by the video controller. Thus, varioustypes of test images may be formed.

Although a few exemplary embodiments of the present general inventiveconcept have been shown and described, it will be appreciated by thoseskilled in the art that changes may be made in these exemplaryembodiments without departing from the principles and spirit of thegeneral inventive concept, the scope of which is defined in the appendedclaims and their equivalents.

1. An image forming apparatus comprising: a transport part whichcomprises a transport belt to transport a printing medium; an imageforming part which transfers a toner to form a color image; and acontroller which controls the image forming part to form a test imagefor color registration of the image forming part on the transport beltwhile an image is formed for a plurality of printing media correspondingto a single printing process.
 2. The image forming apparatus accordingto claim 1, wherein the image forming part comprises: an engine whichperforms an exposure process for the toner to be developed andtransferred; a video controller which generates video data based onprinting data corresponding to the image being formed on the printingmedium or test data corresponding to the test image; and an enginecontroller which operates the engine on the basis of the video datagenerated by the video controller.
 3. The image forming apparatusaccording to claim 2, wherein the engine controller comprises an autocolor registration (ACR) controller which performs the colorregistration of the image forming part according to a result of sensingthe test image.
 4. The image forming apparatus according to claim 2,further comprising a data storage part which stores the test data,wherein the video controller reads out the test data stored in the datastorage part through direct memory access (DMA).
 5. The image formingapparatus according to claim 4, wherein the data storage part furtherstores the printing data.
 6. An image forming apparatus comprising: anengine which transfers a toner to form a color image; a video controllerwhich generates video data; an engine controller which operates theengine according to the video data generated by the video controller;and a controller which controls the video controller to generate videodata based on printing data or test data by determining whether toperform a printing process to form an image on a printing medium or toperform color registration of the engine.
 7. The image forming apparatusaccording to claim 6, wherein the engine controller comprises an autocolor registration (ACR) controller which performs the colorregistration of the engine according to a result of sensing a test imageformed corresponding to the test data.
 8. The image forming apparatusaccording to claim 6, further comprising a data storage part whichstores the test data, wherein the video controller reads out the testdata stored in the data storage part through direct memory access (DMA).9. The image forming apparatus according to claim 8, wherein the datastorage part further stores the printing data.
 10. A control method ofan image forming apparatus which comprises a transport part having atransport belt to transport a printing medium and an image forming partto transfer a toner to form a color image, the control methodcomprising: controlling the image forming part to form an image on afirst printing medium among a plurality of printing media correspondingto a single printing process; controlling the image forming part to forma test image for color registration of the image forming part on thetransport belt after forming the image for the first printing medium;and controlling the image forming part to form an image on a secondprinting medium among the plurality of the printing media after formingthe test image.
 11. The control method of the image forming apparatusaccording to claim 10, wherein the image forming part comprises: anengine which performs an exposure process for the toner to be developedand transferred; a video controller which generates video data; and anengine controller which operates the engine according to the video datagenerated by the video controller, the controlling the image formingpart to form the image on the first printing medium, the transport beltand the second printing medium comprising controlling the videocontroller to generate video data based on printing data or test datafor color registration according to whether the image forming partperforms the printing process to form the image on the printing mediumor the color registration.
 12. The control method of the image formingapparatus according to claim 11, wherein the engine controller comprisesan auto color registration (ACR) controller which performs the colorregistration of the image forming part, the control method furthercomprising: controlling the ACR controller to perform the colorregistration of the image forming part according to a result of sensingthe test image.
 13. The control method of the image forming apparatusaccording to claim 11, wherein the image forming apparatus furthercomprises a data storage part which stores the test data, thecontrolling the image forming part to form the test image comprisingcontrolling the video controller to read out the test data stored in thedata storage part through direct memory access (DMA).
 14. The controlmethod of the image forming apparatus according to claim 13, wherein thedata storage part further stores the printing data, the controlling theimage forming part to form the image on the first printing medium andthe second printing medium comprising controlling the video controllerto read out the printing data stored in the data storage part throughdirect memory access (DMA).
 15. A control method of an image formingapparatus which comprises an engine to transfer a toner to form a colorimage, a video controller to generate video data and an enginecontroller to operate the engine according to the video data generatedby the video controller, the control method comprising: determiningwhether to perform a printing process to form an image on a printingmedium or to perform color registration of the engine; and controllingthe video controller to generate the video data based on printing dataor test data respectively corresponding to the determined printingprocess or color registration.
 16. The control method of the imageforming apparatus according to claim 15, wherein the engine controllercomprises an auto color registration (ACR) controller which performs thecolor registration of the engine, the control method further comprisingcontrolling the auto color registration controller to perform the colorregistration of the engine according to a result of sensing a test imageformed corresponding to the test data.
 17. The control method of theimage forming apparatus according to claim 15, wherein the image formingapparatus further comprises a data storage part which stores the testdata, the controlling the video controller to generate the video datacomprising controlling the video controller to read out the test datastored in the data storage part through direct memory access (DMA). 18.The control method of the image forming apparatus according to claim 17,wherein the data storage part further stores the printing data, thecontrolling the video controller to generate the video data comprisingcontrolling the video controller to read out the printing data stored inthe data storage part through direct memory access (DMA).
 19. An imageforming apparatus comprising: an image forming part which forms a colorimage for a plurality of printing media; and a controller which controlsthe image forming part during a printing process to form a test imagefor color registration after forming an image on a first printing mediumand before forming another image on a second printing medium.
 20. Theimage forming apparatus according to claim 19, wherein the controlleroutputs a control signal to form the test image within an idle timeduring the printing process.
 21. The image forming apparatus accordingto claim 19, wherein the image forming part comprises: an engine whichperforms an exposure process for a toner to be developed andtransferred; a video controller which generates video data based onprinting data corresponding to the image being formed on one of theplurality of printing media or test data corresponding to the testimage; and an engine controller which operates the engine based on videodata generated by the video controller.
 22. The image forming apparatusaccording to claim 21, wherein the video controller reads out the testdata stored in a data storage part during the printing process.
 23. Theimage forming apparatus according to claim 19, wherein the image formingpart forms the test image for color registration during the firstprinting medium output time during the printing process.
 24. The imageforming apparatus according to claim 21, wherein the engine controllerperforms the color registration during the printing process.